I briefly stuck one severely underdriven on 4AA's on top of a 5W just to check out the beam. Donut hole /ubbthreads/images/graemlins/grin.gif I heard that optimizing the distance between the LED and optic can minimize this but if I have to worry about that AND centering the LED, then it's not worth it. Just trying to center it is a PITA all by itself.
CM